Getting up to Speed on Laser-Plasma Interactions

When NIF & Photon Science summer scholar Joshua Ludwig reported to the Lab in May, his mentor Pierre Michel was concerned that he had "completely overwhelmed" the plasma physics graduate student with information about his projects.

But the 25-year-old Ludwig wasn’t fazed. Instead, he learned quickly and earned high praise for his work on the use of high-bandwidth lasers for plasma photonics experiments related to inertial confinement fusion (ICF) and high energy density (HED) research.

"The amount and quality of the work he produced just during these two months is what we would normally expect from an experienced staff scientist, perhaps even better," said Michel, the NIF & Photon Science laser-plasma applications group leader.

Ludwig, a University of Alberta graduate student, said his assignment fit his academic and personal interests.

"I have some experience with Fourier transforms (a method of representing a waveform), so it came natural to work though that stuff fairly quickly," Ludwig said. "I love programming, too. I do that as a hobby. In the evenings, I’ll work on that stuff at home just for fun."

This summer is Ludwig’s third at the Lab. He previously worked on a project aimed at increasing the effective distance for laser wakefield acceleration, which uses a high-intensity short laser pulse to generate waves in a plasma, accelerating electrons like surfers over ocean waves.

He was the first author of a Physics of Plasmas paper published this spring on the results of that research, which showed that a second lower-power laser beam traveling in the opposite direction can help maintain the first wave-generating laser as it loses energy and spreads in space.

This year, Michel asked Ludwig to focus on something different: investigating new ways to achieve high bandwidth on high-power lasers, applying those lasers for plasma photonics experiments, and mitigating laser-plasma instabilities in ICF and HED experiments.

"As soon as I got here, we were looking at speckle (nonuniformity, or "hot spot") movement on the NIF laser," Ludwig said. "I wrote a code that simulates different optical elements from NIF and then we used it to characterize the speckle movement to see how we can speed it up to prevent laser-plasma instabilities."

"It was along the lines of stuff that interested me," he said. "I have some experience with signal processing and my bachelor’s degree was actually in geophysics. That prepared me for that kind of stuff."

He said much of his work with laser light propagation through optical components "takes advantage of the computational speed and mathematical relations of the Fourier transform."

Michel said he was surprised at how fast Ludwig got up to speed.

"He absorbed it in an incredible amount of time," Michel said. "I really didn’t expect he would get it so quickly."

Intuition for Physics

Ludwig has an inner drive and "intuition for physics" that lets him quickly process large amounts of information, Michel said. "When he has a big, complicated program, he is able to break it down into smaller pieces that are easier to manage one by one."

In early July, Ludwig travelled to Maine to represent the Lab at the Anomalous Absorption Conference, a small but prestigious gathering of the world’s top laser-plasma interaction (LPI) experts.

He delivered a poster on the "design of a high-bandwidth probe laser for LPI and plasma photonics experiments." Michel said his colleagues at the conference told him they thought Ludwig presented the best poster overall.

"He’s very enthusiastic," Michel said. "He’s also very mellow and a very nice guy, but at the same time, he’s very driven."

Perhaps that’s why Ludwig, who grew up in the Canadian city of Red Deer in central Alberta, was drawn to the Bay Area.

"I’ve always wanted to live in California, even as a kid growing up," he said. When the Lab internships came up, he said, "it was kind of a no-brainer when I got the opportunity."

He’ll be getting more time here: Ludwig has agreed to an offer for an extended appointment as a temporary student intern until next May. He then hopes to have another stint as a summer scholar after that before returning to Alberta to finish his PhD.

And after that, he might want to return again to the Lab, which he first learned about in high school when he watched a BBC documentary on NIF.

"I would love to work on NIF," Ludwig said. "Working on something related to fusion would be pretty cool. It’s something we need, so whatever I could contribute to that would be great."